1. Field of the Invention
The present invention relates to a temperature sensor for measuring the temperature of a fluid, such as exhaust gas or intake gas.
2. Description of the Related Art
Conventionally, a temperature sensor having a heat-sensitive portion whose electric characteristic varies with temperature is known. The temperature sensor is attached to, for example, an exhaust pipe of an automotive engine and is adapted to measure the temperature of exhaust gas flowing through the exhaust pipe. The heat-sensitive portion of the temperature sensor is composed of, for example, a thermistor sintered-body whose resistance varies with temperature. A pair of electrodes for detecting the resistance of the heat-sensitive portion is disposed in such a manner that the heat-sensitive portion is sandwiched therebetween. The heat-sensitive portion and the pair of electrodes are sealed in a seal portion formed of glass or the like, thereby forming a heat-sensitive element. An insulating support for supporting the heat-sensitive element is provided on the rear side of the heat-sensitive element. An insulation sheath is provided on the rear side of the insulating support. The insulation sheath allows for wires electrically connected to the paired electrodes to extend therethrough. Temperature is measured from the resistance of the heat-sensitive portion detected by means of the pair of electrodes.
In order to improve responsiveness of the temperature sensor, various studies have been conducted. For example, according to the temperature sensor disclosed in Patent Document 1, the distance between the heat-sensitive portion (thermistor element) and a housing tube which accommodates the heat-sensitive portion is set to 0.3 mm or less, thereby improving the heat-receiving rate of the heat-sensitive portion. According to the temperature sensor disclosed in Patent Document 2, a distal end portion of the housing tube which accommodates the heat-sensitive portion is thin-walled as compared with the other portion of the housing tube. By employing a thin-walled distal end portion of the housing tube, heat is quickly transferred to the heat-sensitive portion from outside the housing tube.
[Patent Document 1] Japanese Patent Application Laid-Open (kokai) No. 2002-350241
[Patent Document 2] Japanese Patent Application Laid-Open (kokai) No. 2010-32237
3. Problems to be Solved by the Invention
In a certain temperature sensor, the heat-sensitive element, the insulating support and the insulation sheath are sequentially disposed from the distal side such that they contact one another directly or via another member. That is, the heat-sensitive element, the insulating support, and the insulation sheath are disposed in a thermally coupled condition. In this case, heat transfer of heat from the heat-sensitive element toward the rear side through the insulating support and the insulation sheath is apt to arise. The occurrence of such heat transfer increases the time that it takes the temperature of the heat-sensitive portion to reach that of a measurement object. The techniques described in Patent Documents 1 and 2 encounter difficulty in restraining deterioration in responsiveness of the temperature sensor caused by the heat transfer.